Titanium oxide particle, composition for forming photocatalyst, and photocatalyst

ABSTRACT

A titanium oxide particle includes a metal having a hydrocarbon group, which is bonded to a surface of the titanium oxide particle through an oxygen atom, and absorbs light having a wavelength of 450 nm and light having a wavelength of 750 nm, wherein an element ratio C/Ti between carbon C and titanium Ti in a surface of the titanium oxide particle is from 0.3 to 1.2, and a reduced amount of C/Ti on the surface of the titanium oxide particle before and after irradiation with an ultraviolet ray having a wavelength of 352 nm and at an irradiation intensity of 1.3 mW/cm2 for 20 hours is from 0.1 to 0.9.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2016-240463 filed Dec. 12, 2016.

BACKGROUND Technical Field

The present invention relates to a titanium oxide particle, acomposition for forming a photocatalyst, and a photocatalyst.

SUMMARY

According to an aspect of the invention, there is provided a titaniumoxide particle,

-   -   which includes a metal having a hydrocarbon group, which is        bonded to a surface of the titanium oxide particle through an        oxygen atom, and    -   absorbs light having a wavelength of 450 nm and light having a        wavelength of 750 nm,    -   wherein an element ratio C/Ti between carbon C and titanium Ti        on a surface of the titanium oxide particle is from 0.3 to 1.2,        and    -   a reduced amount of C/Ti on the surface of the titanium oxide        particle before and after irradiation with an ultraviolet ray        having a wavelength of 352 nm and at an irradiation intensity of        1.3 mW/cm² for 20 hours is from 0.1 to 0.9.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment which is an example of theinvention will be described.

Titanium Oxide Particle

A titanium oxide particle according to the exemplary embodiment issubjected to surface treatment with a metal-containing compound whichhas a hydrocarbon group, and absorbs light having wavelengths of 450 nmand 750 nm in a visible absorption spectrum. In the titanium oxideparticle, an element ratio C/Ti between carbon C and titanium Ti on thesurface thereof is from 0.3 to 1.2. In a case where the titanium oxideparticle is irradiated with an ultraviolet ray having a wavelength of352 nm at an irradiation intensity of 1.3 mW/cm² for 20 hours, a reducedamount of the C/Ti element ratio on the surface of the titanium oxideparticle before and after the irradiation with the ultraviolet ray isfrom 0.1 to 0.9.

The titanium oxide particle according to the exemplary embodiment isappropriately used as a photocatalyst.

Since the titanium oxide particle according to the exemplary embodimenthas the above configuration, the titanium oxide particle also shows ahigh photocatalyst function even in a visible light region. The reasonis guessed as follows.

Firstly, generally, an untreated titanium oxide particle as aphotocatalyst absorbs ultraviolet light, and thus shows a photocatalystfunction (photocatalyst activation). Thus, the untreated titanium oxideparticle shows the photocatalyst function during a daytime on a sunnyday on which sufficient ultraviolet light may be secured, but it isdifficult that the untreated titanium oxide particle sufficiently showsthe photocatalyst function during a night-time or in the shade. Forexample, in a case where the untreated titanium oxide particle is usedas an exterior wall material, there is a tendency of stain resistancebeing deteriorated in accordance with a sunny place and a shade place.In a case where the untreated titanium oxide particle is used in an aircleaner, a water purifier, or the like, an additional mounting space,for example, in which a black light and the like which function as alight source of an ultraviolet ray is mounted in the device, may berequired.

Recently, titanium oxide particles which show the photocatalyst function(photocatalyst activation) by absorbing visible light are also known.For example, a titanium oxide particle obtained by making a differenttype of metal (iron, copper, tungsten, or the like) adhere to titaniumoxide, and a titanium oxide particle obtained by doping a nitrogenelement, a sulfur element, or the like are known as such a visiblelight-absorption type titanium oxide particle. If the photocatalystfunction is highly shown, there is a problem, for example, in that abinder such as an organic resin, which is used for fixing aphotocatalyst material to the surface of a base material is decomposedand the base material itself is deteriorated.

Most of titanium oxide photocatalyst materials which have been knownuntil now are hydrophilic. Thus, the materials have a tendency of lowaffinity with an organic or inorganic binder used for fixing a material,and particles are easily aggregated. Thus, a problem of deterioration ofphotocatalyst performance or separation from the binder easily hasoccurred. A method of treating the surface of a material with a surfacetreatment agent and the like is provided for this problem. If thismethod is performed, aggregation of particles or dispersibility into abinder is improved, but the surface treatment agent covers the surfaceof the photocatalyst material, thereby deteriorating the photocatalystperformance.

Accordingly, a titanium oxide particle which has small particlecohesiveness, good dispersibility into a binder, and a highphotocatalyst function which is shown even in a visible light region isrequired.

For the requirement thereof, there is provided a titanium oxide particlesubjected to surface treatment with a metal-containing compound whichhas a hydrocarbon group. The titanium oxide particle absorbs lighthaving wavelengths of 450 nm and 750 nm in an ultraviolet visibleabsorption spectrum. A C/Ti element ratio on the surface of the titaniumoxide particle is set to be from 0.3 to 1.2. In addition, in a casewhere the titanium oxide particle is irradiated with an ultraviolet rayhaving a wavelength of 352 nm and at an irradiation intensity of 1.3mW/cm² for 20 hours, the reduced amount of the C/Ti element ratio on thesurface of the titanium oxide particle before and after the irradiationwith the ultraviolet ray is set to be from 0.1 to 0.9.

The titanium oxide particle which satisfies C/Ti on the surface of theparticle has an appropriate C/Ti in comparison to a general titaniumoxide particle which is subjected to surface treatment with ametal-containing compound which has a hydrocarbon group, or an untreatedtitanium oxide particle.

Since C/Ti on the surface of the titanium oxide particle is from 0.3 to1.2, the carbon content of the hydrocarbon group and the like in thesurface of the titanium oxide particle becomes appropriate. Light havingwavelength of 450 nm and light having wavelength of 750 nm aresufficiently absorbed, and a high photocatalyst function is shown in thevisible light region. Since the carbon content of the hydrocarbon groupor the like on the surface of the titanium oxide particle isappropriate, the particle cohesiveness is small and the dispersibilityinto the binder is improved.

If C/Ti is less than 0.3, the carbon content on the surface of thetitanium oxide particle is small. Thus, light having wavelengths of 450nm and 750 nm is not sufficiently absorbed, the photocatalyst functionin the visible light region is deteriorated, and the particlecohesiveness or the dispersibility into the binder is deteriorated. Inaddition, if the C/Ti element ratio is more than 1.2, the amount of thehydrocarbon group on the surface of the titanium oxide particle islarge. Thus, an exposed amount of a portion at which titanium oxide isactivated on the surface of the titanium oxide particle is reduced andthe photocatalyst function in the visible light region is deteriorated.

In the titanium oxide particle which satisfies the reduced amount ofC/Ti before and after the irradiation with the ultraviolet ray, thereduced amount of C/Ti indicates a large value in comparison to ageneral titanium oxide particle which is subjected to surface treatmentwith a metal-containing compound which has a hydrocarbon group, or anuntreated titanium oxide particle.

Since the reduced amount of C/Ti on the surface of the titanium oxideparticle before and after irradiation with an ultraviolet ray in a casewhere the titanium oxide particle is irradiated with the ultraviolet rayhaving a wavelength of 352 nm at an irradiation intensity of 1.3 mW/cm²for 20 hours is from 0.1 to 0.9, the carbon content of the hydrocarbongroup and the like or the carbon content (carbon) obtained bycarbonizing hydrocarbon, on the surface of the titanium oxide particle,is adequate. In addition, light having wavelength of 450 nm and lighthaving wavelength of 750 nm are sufficiently absorbed, and the highphotocatalyst function is shown in the visible light region. Since thehydrocarbon group and the like on the surface of the titanium oxideparticle is appropriately decomposed by photocatalyst activation of thetitanium oxide particle, deterioration of the binder or the basematerial is prevented.

If the reduced amount of C/Ti is more than 0.9, carbon in thehydrocarbon group or carbon obtained by carbonizing hydrocarbon, on thesurface of the titanium oxide particle, is easily decomposed by thephotocatalyst activation and thus is easily separated from the titaniumoxide particle. Accordingly, the photocatalyst function in the visiblelight region is easily deteriorated. If the reduced amount of C/Ti isless than 0.1, the carbon content on the surface of the titanium oxideparticle is small. Thus, light having a wavelength of 450 nm and lighthaving a wavelength of 750 nm are not sufficiently absorbed and thephotocatalyst function in the visible light region is deteriorated.Since the small amount of the hydrocarbon group and the like on thesurface of the titanium oxide particle is decomposed, a function ofpreventing deterioration of the binder or the base material isdeteriorated.

The titanium oxide particle which satisfies the numerical range for C/Tiand the reduced amount of C/Ti before and after irradiation with anultraviolet ray, on the surface of the particle, is prepared, forexample, in a manner that some hydrocarbon groups in a titanium oxideparticle subjected to surface treatment with a metal-containing compoundwhich has a hydrocarbon group are oxidized and decomposed by treatmentsuch as heating. Regarding such a titanium oxide particle, it isconsidered that hydrocarbon and carbon obtained by carbonizinghydrocarbon are provided in a pore of the titanium oxide particle, thatis, hydrocarbon and carbon obtained by carbonizing hydrocarbon areburied from the surface layer over the inside of the titanium oxideparticle.

It is considered that the buried carbon absorbs visible light along withultraviolet light and functions as a charge separation material and apromotor.

That is, it is considered as follows. Carbon provided in the pore of thetitanium oxide particle accelerates excitation of an electron on thesurface of the titanium oxide particle by absorbing visible light alongwith ultraviolet light, and a probability of recombining the excitedelectron and a hole is reduced. Accordingly, the photocatalyst functionis improved.

Generally, an untreated titanium oxide particle has a tendency of a lowdegree of freedom in control for a particle diameter, particle diameterdistribution, and a particle shape, and a tendency of high particlecohesiveness. Thus, the untreated titanium oxide particle has baddispersibility of the titanium oxide particle in a resin, and, in aliquid, and has a tendency to 1) to be difficult to show thephotocatalyst function, and 2) to easily deteriorate transparency of afilm or the like and uniformity of a film obtained by coating with acoating liquid.

However, since the titanium oxide particle according to the exemplaryembodiment has a hydrocarbon group derived from a metal-containingcompound, on the surface, dispersibility of primary particles in thecoated film is also secured. Thus, a substantially-uniform coated filmmay be formed. Light abuts on the titanium oxide particle with highefficiency and the photocatalyst function is easily shown. Transparencyof a film or the like and uniformity of a film obtained by coating witha coating liquid is also improved, and thus design properties are alsoensured. As a result, for example, when the surface of an exterior wallmaterial, a plate, a pipe, and nonwoven fabric (nonwoven fabric made ofceramics or the like) is coated with a coating material including thetitanium oxide particle, an occurrence of aggregation of titanium oxideparticles and an occurrence of coating defects are prevented, and thephotocatalyst function is easily shown for a long term.

From the above descriptions, it is guessed that, with the aboveconfiguration, the titanium oxide particle according to the exemplaryembodiment has excellent particle dispersibility, and shows the highphotocatalyst function even in the visible light region.

Details of the titanium oxide particle according to the exemplaryembodiment will be described below.

Untreated Titanium Oxide Particle

Examples of an untreated titanium oxide particle (titanium oxideparticle as a target of surface treatment) include particles of titaniumoxide of a brookite type, an anatase type, a rutile type, and the like.The titanium oxide particle may have a single crystal structure ofbrookite, anatase, rutile, and the like or may have a mixed crystalstructure in which the above crystals are provided together.

The untreated titanium oxide particle according to the exemplaryembodiment is a titanium oxide particle which is not subjected tosurface treatment with a metal-containing compound having a hydrocarbongroup. The surface treatment may include any type of surface treatment.However, it is preferable that the titanium oxide particle according tothe exemplary embodiment is a titanium oxide particle subjected tosurface treatment with only a metal-containing compound having ahydrocarbon group.

A preparing method of the untreated titanium oxide particle is notparticularly limited. However, a chlorine method (vapor phase method),and a sulfuric acid method (liquid phase method) are exemplified.

An example of the chlorine method (vapor phase method) is as follows.Firstly, rutile ore which is a raw material is caused to react with cokeand chlorine. After the reactant is exposed to gaseous titaniumtetrachloride once, cooling is performed, thereby a titaniumtetrachloride liquid is obtained. Then, obtained titanium tetrachlorideliquid is caused to react with oxygen at a high temperature, and then achlorine gas is separated. Thus, an untreated titanium oxide isobtained.

An example of the sulfuric acid method (liquid phase method) is asfollows. Firstly, ilmenite ore (FeTiO₃) or titanium slag which is a rawmaterial is dissolved in concentrated sulfuric acid, and an ironcomponent which is an impurity is separated in a form of iron sulfate(FeSO₄), thereby titanium oxysulfate (TiOSO₄) is obtained. Then,titanium oxysulfate (TiOSO₄) is subjected to hydrolysis, and thus isprecipitated in a form of titanium oxyhydroxide (TiO(OH)₂). Thisprecipitate is washed and dried, and a dried matter is baked. Thus, anuntreated titanium oxide is obtained.

As a method of preparing an untreated titanium oxide particle,additionally, a sol-gel method using titanium alkoxide and a method ofbaking metatitanic acid are provided. Regarding a crystal structure ofthe titanium oxide particle, the crystal structure is changed tobrookite, anatase, or rutile by a baking temperature (for example,heating in a range of 400° C. to 1,200° C.). Thus, an untreated titaniumoxide particle having a desired crystal structure is obtained by thebaking temperature.

Metal-Containing Compound

The metal-containing compound has a hydrocarbon group. As a hydrocarbongroup included in the metal-containing compound, an aliphatichydrocarbon group or an aromatic hydrocarbon group which has 1 to 20carbon atoms (preferably 1 to 18 carbon atoms, more preferably 4 to 12carbon atoms, and further preferably 4 to 10 carbon atoms) and issaturated or unsaturated is exemplified.

The hydrocarbon group may or may not be directly combined to metal inthe metal-containing compound. However, from a viewpoint of showing ahigh photocatalyst function and improving dispersibility, thehydrocarbon group is preferably directly combined.

As metal of the metal-containing compound having the hydrocarbon group,a metal atom selected from the group consisting of silicon, titanium,and aluminum is preferable, and silicon is particularly preferable. Thatis, as the metal-containing compound having a hydrocarbon group, asilane compound having a hydrocarbon group is particularly preferable.

Examples of the silane compound include a chlorosilane compound, analkoxysilane compound, and a silazane compound (hexamethyldisilazane andthe like).

Among these substances, from a viewpoint of showing a high photocatalystfunction and improving dispersibility, a compound represented by aformula of R¹ _(n)SiR² _(m) is preferable as the silane compound.

In the formula of R¹ _(n)SiR² _(m), R¹ represents an aliphatichydrocarbon group or an aromatic hydrocarbon group which has 1 to 20carbon atoms and is saturated or unsaturated, R² represents a halogenatom or an alkoxy group, n represents an integer of 1 to 3, and mrepresents an integer of 1 to 3, provided that n+m=4 is satisfied. In acase where n represents an integer of 2 or 3, plural R¹s may be the sameor different. In a case where m represents an integer of 2 or 3, pluralR²s may be the same or different.

The aliphatic hydrocarbon group represented by R¹ may have any of astraight chain shape, a branched chain shape, and a ring shape. However,from a viewpoint of dispersibility, a straight chain shape or a branchedchain shape is preferable, and a straight chain shape is morepreferable. From a viewpoint of showing a high photocatalyst functionand improving dispersibility, the aliphatic hydrocarbon group haspreferably from 1 to 18 carbon atoms, more preferably from 4 to 12carbon atoms, and further preferably from 4 to 10 carbon atoms. Thealiphatic hydrocarbon group may be a saturated or unsaturated aliphatichydrocarbon group. However, from a viewpoint of showing a highphotocatalyst function and improving dispersibility, a saturatedaliphatic hydrocarbon group is preferable, and an alkyl group is morepreferable.

Examples of the saturated aliphatic hydrocarbon group include astraight-chain alkyl group (a methyl group, an ethyl group, a propylgroup, a butyl group, a pentyl group, a hexyl group, a heptyl group, anoctyl group, a nonyl group, a decyl group, a dodecyl group, a hexadecylgroup, an icosyl group, and the like); a branched chain alkyl group (anisopropyl group, an isobutyl group, an isopentyl group, a neopentylgroup, a 2-ethylhexyl group, a tertiary butyl group, a tertiary pentylgroup, an isopentadecyl group, and the like); and a cyclic alkyl group(a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, acycloheptyl group, a cyclooctyl group, a tricyclodecyl group, anorbornyl group, an adamantyl group, and the like).

Examples of the unsaturated aliphatic hydrocarbon group include analkenyl group (a vinyl group (ethenyl group), a 1-propenyl group, a2-propenyl group, a 2-butenyl group, a 1-butenyl group, a 1-hexenylgroup, a 2-dodecenyl group, a pentenyl group, and the like); and analkynyl group (an ethynyl group, a 1-propynyl group, a 2-propynyl group,a 1-butynyl group, a 3-hexynyl group, a 2-dodecynyl group, and thelike).

The aliphatic hydrocarbon group also includes a substituted aliphatichydrocarbon group. Examples of a substituent which may be substitutedwith the aliphatic hydrocarbon group include an epoxy group, a mercaptogroup, a methacryloyl group, and an acryloyl group.

As the aromatic hydrocarbon group represented by R¹, an aromatichydrocarbon group having 6 to 27 carbon atoms (preferably 6 to 18) isexemplified.

Examples of the aromatic hydrocarbon group include a phenyl group, abiphenyl group, a terphenyl group, a naphthalenyl group, and ananthracenyl group.

The aromatic hydrocarbon group also includes a substituted aromatichydrocarbon group. Examples of the substituent which the aromatichydrocarbon group may have include an epoxy group, a glycidyl group, amercapto group, a methacryloyl group, and an acryloyl group.

Examples of the halogen atom represented by R² include a fluorine atom,a chlorine atom, a bromine atom, and an iodine atom. Among these atoms,as the halogen atom, a chlorine atom, a bromine atom, or an iodine atomis preferable.

Examples of the alkoxy group represented by R² include an alkoxy grouphaving 1 to 10 carbon atoms (preferably 1 to 8, and more preferably 3 to8).

Examples of the alkoxy group include a methoxy group, an ethoxy group,an isopropoxy group, a t-butoxy group, a n-butoxy group, a n-hexyloxygroup, a 2-ethylhexyloxy group, and a 3,5,5-trimethylhexyloxy group.

The alkoxy group also includes a substituted alkoxy group. Examples ofthe substituent which the alkoxy group may have include a halogen atom,a hydroxyl group, an amino group, an alkoxy group, an amide group, and acarbonyl group.

As the compound represented by the formula of R¹ _(n)SiR² _(m), acompound in which R¹ represents a saturated hydrocarbon group ispreferable from a viewpoint of showing a high photocatalyst function andimproving dispersibility. In particular, as the compound represented bythe formula of R¹ _(n)SiR² _(m), a compound in which R¹ represents asaturated aliphatic hydrocarbon group having 1 to 20 carbon atoms, R²represents a halogen atom or an alkoxy group, n represents an integer of1 to 3, and m represents an integer of 1 to 3, provided that n+m=4 issatisfied, is preferable.

Specific examples of the compound represented by the formula of R¹_(n)SiR² _(m) include vinyltrimethoxysilane, propyl trimethoxysilane,i-butyltrimethoxysilane, n-butyltrimethoxysilane,n-hexyltrimethoxysilane, n-octyltrimethoxysilane,n-dodecyltriethoxysilane, phenyltrimethoxysilane,3-glycidoxypropyltrimethoxysilane, tetramethoxysilane,methyltrimethoxysilane, dimethyl dimethoxysilane,diphenyldimethoxysilane, o-methylphenyltrimethoxysilane,p-methylphenyltrimethoxysilane, decyltrimethoxysilane,dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane,dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane,i-butyltriethoxysilane, decyltriethoxysilane, vinyl triethoxysilane,γ-methacryloxypropyltrimethoxysilane,γ-glycidyloxypropylmethyldimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane,γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane,γ-(2-aminoethyl) aminopropyltrimethoxysilane, and γ-(2-aminoethyl)aminopropylmethyldimethoxysilane.

The silane compound may be singly used or may be used in combination oftwo types or more.

Among these substances, from a viewpoint of showing a high photocatalystfunction and improving dispersibility, the hydrocarbon group in thesilane compound is preferably an aliphatic hydrocarbon group, morepreferably a saturated aliphatic hydrocarbon group, and particularlypreferably an alkyl group.

From a viewpoint of showing a high photocatalyst function and improvingdispersibility, the hydrocarbon group in the silane compound haspreferably 1 to 18 carbon atoms, more preferably 4 to 12 carbon atoms,and particularly preferably 4 to 10 carbon atoms.

Examples of a titanium compound which has Ti as a metal atom in themetal-containing compound and has a hydrocarbon group include a titanatecoupling agent such as isopropyl triisostearoyl titanate, tetraoctylbis(ditridecyl phosphite)titanate, and bis(dioctylpyrophosphate)oxyacetate titanate; and titanium chelate such asdi-i-propoxy bis(ethyl acetoacetate) titanium, di-i-propoxybis(acetylacetonato)titanium, di-i-propoxybis(triethanolaminate)titanium, di-i-propoxy titanium diacetate, anddi-i-propoxy titanium dipropionate.

Examples of an aluminum compound which has a metal atom of themetal-containing compound is Al and has a hydrocarbon group includealkyl aluminate such as triethoxyaluminum, tri-i-propoxyaluminum, andtri-sec-butoxyaluminum; aluminum chelate such asdi-i-propoxy.mono-sec-butoxyaluminum, anddi-i-propoxyaluminum.ethylacetoacetate; and an aluminum coupling agentsuch as acetoalkoxyaluminum diisopropylate.

Characteristics of Titanium Oxide Particle

The titanium oxide particle according to the exemplary embodimentabsorbs light having wavelengths of 450 nm and 750 nm in a visibleabsorption spectrum.

From a viewpoint of showing a high photocatalyst function even in thevisible light region, it is preferable that the titanium oxide particleaccording to the exemplary embodiment absorbs light having wavelengthsof 450 nm, 600 nm, and 750 nm in the visible absorption spectrum. It ismore preferable that the titanium oxide particle absorbs light having awhole range of a wavelength of 450 nm to 750 nm in the visibleabsorption spectrum. It is particularly preferable that the titaniumoxide particle absorbs light having a whole range of a wavelength of 400nm to 800 nm in the visible absorption spectrum.

Regarding the titanium oxide particle, from a viewpoint of showing ahigh photocatalyst function even in the visible light region, in theultraviolet visible absorption spectrum, when an absorbance at awavelength of 350 nm is set to 1, the absorbance at a wavelength of 450nm is preferably equal to or more than 0.02 (preferably equal to or morethan 0.1). In addition, it is more preferable that an absorbance at awavelength of 450 nm is equal to or more than 0.2 (preferably equal toor more than 0.3), and an absorbance at a wavelength of 750 nm is equalto or more than 0.02 (preferably equal to or more than 0.1).

The ultraviolet visible absorption spectrum is measured by a method asfollows. Firstly, a titanium oxide particle as a measurement target isdispersed in tetrahydrofuran, and then the resultant dispersion isapplied onto a glass substrate and drying is performed at 24° C. in theair. Measurement is performed in arrangement of diffusion andreflection, and theoretical absorbance is obtained by Kubelka-Munkconversion. Regarding a diffusion and reflection spectrum, measurementis performed on a range of a wavelength from 200 nm to 900 nm by usingreflectance and by using a spectrophotometer (U-4100 manufactured byHitachi High-Technologies Corporation) [measured under measurementconditions; a scan speed of 600 nm, a slit width of 2 nm, and a samplinginterval of 1 nm, in a total-reflectance measurement mode]. Then,Kubelka-Munk conversion is performed so as to obtain a visibleabsorption spectrum.

The titanium oxide particle according to the exemplary embodiment hasC/Ti of 0.3 to 1.2 on the surface thereof. In a case where the titaniumoxide particle is irradiated with the ultraviolet ray having awavelength of 352 nm and at an irradiation intensity of 1.3 mW/cm² for20 hours, the changed amount of C/Ti on the surface of the titaniumoxide particle before and after the irradiation with the ultraviolet rayis from 0.1 to 0.9.

Specifically, for example, from a viewpoint of showing a highphotocatalyst function even in the visible light region, the C/Ti on thesurface of the titanium oxide particle is preferably from 0.4 to 1.1,more preferably from 0.5 to 1.0, and particularly preferably from 0.6 to0.9.

The changed amount of C/Ti on the surface of the particle before andafter the irradiation with an ultraviolet ray is preferably from 0.2 to0.85 and more preferably from 0.25 to 0.8.

C/Ti on the surface of the titanium oxide particle is measured by amethod as follows. Firstly, measurement is performed on the titaniumoxide particle as a measurement target by using an X-ray photoelectronspectroscopy (XPS) analyzer (JPS-9000MX manufactured by JEOL Ltd.). Themeasurement is performed in a manner that a MgKα ray is used as an X-raysource, an acceleration voltage is set to 10 kV, and an emission currentis set to 20 mA. C/Ti is calculated from intensity at a peak of eachelement.

Regarding irradiation of the surface of the titanium oxide particle withan ultraviolet ray, irradiation is performed with an ultraviolet rayhaving a wavelength of 352 nm and at an irradiation intensity of 1.3mW/cm². It is assumed that irradiation is performed under the conditionswhere the temperature of the titanium oxide particle when irradiationwith an ultraviolet ray starts is from 15° C. to 30° C. and anirradiation time is 20 hours.

After the irradiation with the ultraviolet ray, C/Ti is measured by theabove-described method and the reduced amount of C/Ti before and afterthe irradiation with the ultraviolet ray is calculated.

The volume average particle diameter of titanium oxide particlesaccording to the exemplary embodiment is preferably 10 nm to 1 μm, morepreferably 10 nm to 200 nm, and further preferably 15 nm to 200 nm.

If the volume average particle diameter of the titanium oxide particlesis equal to or more than 10 nm, aggregation of the titanium oxideparticles is prevented, and the photocatalyst function is easily highlyshown. If the volume average particle diameter of the titanium oxideparticles is set to be equal to or less than 1 μm, a percentage of aspecific surface area to an amount is increased, and the photocatalystfunction is easily highly shown. Thus, if the volume average particlediameter of the titanium oxide particles is set to be in the aboverange, a high photocatalyst function is easily shown in the visiblelight region.

The volume average particle diameter of the titanium oxide particles ismeasured by NANOTRACK UPA-ST (a dynamic light scattering type particlediameter measuring device manufactured by Microtrac Bel). Regarding ameasurement condition, the concentration of a sample is set to be 20%,and a measurement period is set to be 300 seconds. This device measuresa particle diameter by using a Brownian motion in dispersoid. The deviceirradiates a solution with a laser beam, and detects scattered light, soas to measure a particle diameter.

Cumulative distribution of a volume of each particle from a smallparticle diameter side, in a divided particle diameter range (channel)is drawn based on particle diameter distribution which is measured by adynamic light scattering type particle diameter measuring device. Then,a particle diameter causing the accumulation to be 50% is obtained as avolume average particle diameter.

Preparing Method of Titanium Oxide Particle

A preparing method of the titanium oxide particle according to theexemplary embodiment is not particularly limited. However, it ispreferable that the preparing method includes a process of performingsurface treatment on an untreated titanium oxide particle with ametal-containing compound having a hydrocarbon group, and a process ofheating the titanium oxide particle during or after the process ofperforming surface treatment on the untreated titanium oxide particle.

Firstly, surface treatment of an untreated titanium oxide particle witha metal-containing compound will be described.

A method of performing surface treatment on an untreated titanium oxideparticle with a metal-containing compound is not particularly limited.For example, a method in which a metal-containing compound itself isbrought into contact with an untreated titanium oxide particle, and amethod in which a treatment liquid in which the metal-containingcompound is dissolved in a solvent is brought into contact with anuntreated titanium oxide particle are exemplified. Specifically, forexample, a method in which a metal-containing compound itself or atreatment liquid is added to a dispersion in which untreated titaniumoxide particles are dispersed in a solvent, under stirring, and a methodin which addition (dropping, ejecting, and the like) to an untreatedtitanium oxide particle being in a state of flowing with stirring byHENSCHEL MIXER or the like is performed are exemplified.

With the above method, a reactive group (for example, a hydrolyzablegroup) in the metal-containing compound reacts with a hydrolyzable group(a hydroxyl group, a halogeno group, an alkoxy group, and the like)present on the surface of an untreated titanium oxide particle, and thusthe surface treatment of the untreated titanium oxide particle with themetal-containing compound is performed.

Here, examples of a solvent for dissolving the metal-containing compoundinclude an organic solvent (for example, a hydrocarbon solvent, an estersolvent, an ether solvent, a halogen solvent, and an alcohol solvent),water, and a solvent mixture thereof.

Examples of the hydrocarbon solvent include toluene, benzene, xylene,hexane, octane, hexadecane, and cyclohexane. Examples of the estersolvent include methyl acetate, ethyl acetate, isopropyl acetate, andamyl acetate. Examples of the ether solvent include dibutyl ether anddibenzyl ether. Examples of the halogen solvent include1,1-dichloro-1-fluoroethane, 1,1-dichloro-2,2,2-trifluoroethane,1,1-dichloro-2,2,3,3,3-pentafluoropropane, chloroform, dichloroethane,and carbon tetrachloride. Examples of the alcohol solvent includemethanol, ethanol, and i-propyl alcohol. Examples of the water includetap water, distilled water, and pure water.

As the solvent, in addition to the above solvents, a solvent such asdimethylformamide, dimethylacetamide, dimethylsulfoxide, acetic acid,and sulfuric acid may be used.

In the treatment liquid in which the metal-containing compound isdissolved in a solvent, the concentration of the metal-containingcompound is preferably 0.05 mol/L to 500 mol/L, and more preferably 0.5mol/L to 10 mol/L.

Regarding the condition for surface treatment of a titanium oxideparticle with the metal-containing compound, from a viewpoint of showinga high photocatalyst function and improving dispersibility, thefollowing conditions may be provided. An untreated titanium oxideparticle may be subjected to surface treatment with a metal-containingcompound which is 10% by weight to 100% by weight (preferably, 20% byweight to 75% by weight, and more preferably 25% by weight to 50% byweight) with respect to the untreated titanium oxide particle. If thetreated amount of the metal-containing compound is set to be equal to ormore than 10% by weight, a high photocatalyst function is easier showneven in the visible light region, and the dispersibility is also easilyimproved. If the treated amount of the metal-containing compound is setto be equal to or less than 100% by weight, metal (M) is prevented frombeing present on the surface (Ti—O—) of the titanium oxide particle inan excessive amount, and deterioration of the photocatalyst function bysurplus silicon (Si) is easily prevented.

The temperature of the surface treatment of an untreated titanium oxideparticle with the metal-containing compound is preferably 15° C. to 150°C., and more preferably 20° C. to 100° C. The surface treatment periodis preferably 10 minutes to 120 minutes, and more preferably 30 minutesto 90 minutes.

After the surface treatment of an untreated titanium oxide particle withthe metal-containing compound, drying treatment may be performed. Amethod of the drying treatment is not particularly limited. For example,a known drying method such as a vacuum drying method and a spray dryingmethod is used. A drying temperature is preferably 20° C. to 150° C.

Next, heating treatment will be described.

The heating treatment is performed in the middle of the process ofperforming surface treatment on an untreated titanium oxide particle orperformed after the process of performing surface treatment on anuntreated titanium oxide particle. Specifically, when an untreatedtitanium oxide particle is surface-treated with the metal-containingcompound, when drying treatment after surface treatment is performed, orafter drying treatment, the heating treatment may be separatelyperformed. However, because the titanium oxide particle is required tosufficiently react with the metal-containing compound before the heatingtreatment is performed, the heating treatment is preferably separatelyperformed when drying treatment after surface treatment is performed orafter the drying treatment. It is more preferable that the heatingtreatment is separately performed after the drying treatment isperformed in order that surface treatment and drying of the titaniumoxide particle are appropriately performed.

From a viewpoint of showing a high photocatalyst function and improvingdispersibility, a temperature of the heating treatment is preferably180° C. to 500° C., more preferably 200° C. to 450° C., and furtherpreferably 250° C. to 400° C.

In a case where heating treatment is performed in the middle of theprocess of performing surface treatment on an untreated titanium oxideparticle, the metal-containing compound is caused to sufficiently reactat the temperature of the surface treatment which has been performed inadvance, and then, heating treatment is performed at the temperature ofthe heating treatment. In a case where heating treatment is performed indrying treatment after surface treatment, the temperature of the dryingtreatment is used as the temperature of the heating treatment.

From a viewpoint of showing a high photocatalyst function and improvingdispersibility, a period for the heating treatment is preferably 10minutes to 300 minutes, and more preferably 30 minutes to 120 minutes.

The method of the heating treatment is not particularly limited. A knownheating method, for example, heating by an air furnace, a kiln (rollerhearth kiln, shuttle kiln, or the like), a radiant heating furnace, andthe like, heating by a laser beam, an infrared ray, UV, a microwave, orthe like is used.

With the above processes, the titanium oxide particle according to theexemplary embodiment is appropriately obtained.

Composition for Forming Photocatalyst

A composition for forming a photocatalyst according to the exemplaryembodiment contains the titanium oxide particle according to theexemplary embodiment and at least one compound selected from the groupconsisting of a dispersion medium and a binder.

Examples of a form of the composition for forming a photocatalystaccording to the exemplary embodiment include a dispersion whichcontains the titanium oxide particle according to the exemplaryembodiment and a dispersion medium, and a composition which contains thetitanium oxide particle according to the exemplary embodiment, and anorganic or inorganic binder.

The dispersion may have a paste shape having high viscosity.

As the dispersion medium, water, an organic solvent, and the like arepreferably used.

Examples of the water include tap water, distilled water, and purewater.

The organic solvent is not particularly limited, and for example, ahydrocarbon solvent, an ester solvent, an ether solvent, a halogensolvent, and an alcohol solvent are exemplified.

From a viewpoint of dispersion stability and storage stability, thedispersion preferably contains at least one type of compound selectedfrom the group consisting of a dispersing agent and a surfactant. As thedispersing agent and the surfactant, well-known materials are used.

The binder used in the composition is not particularly limited. Examplesof the binder include fluorine resin, silicone resin, polyester resin,acrylic resin, styrene resin, acrylonitrile/styrene copolymer resin,acrylonitrile/butadiene/styrene copolymer (ABS) resin, epoxy resin,polycarbonate resin, polyamide resin, polyamine resin, polyurethaneresin, polyether resin, polysulfide resin, polyphenol resin, a compoundthereof, an organic binder such as resin obtained by silicone-modifyingor halogen-modifying the above resins, and an inorganic binder such as aglass, ceramic, metal powder.

The dispersion may contain the binder in a form of an emulsion.

The composition for forming a photocatalyst according to the exemplaryembodiment may contain other components other than the above-describedcomponents.

Well-known additives are used as the other components, for example, apromotor, a coloring material, a filler, an antiseptic agent, adefoaming agent, an adhesion-enhancing agent, and a thickener areexemplified.

The composition for forming a photocatalyst according to the exemplaryembodiment may singly contain the titanium oxide particle according tothe exemplary embodiment or may contain two types or more of titaniumoxide particles.

In the composition for forming a photocatalyst according to theexemplary embodiment, the content of the titanium oxide particleaccording to the exemplary embodiment is not particularly limited, andmay be appropriately selected in accordance with various forms such as adispersion and a resin composition, and a desired amount of thephotocatalyst.

A preparing method of a photocatalyst using the composition for forminga photocatalyst according to the exemplary embodiment, or a preparingmethod of a structure having the photocatalyst are not particularlylimited, and well-known applying methods are used.

Examples of the applying method of the composition for forming aphotocatalyst according to the exemplary embodiment include a spincoating method, a dip coating method, a flow coating method, a spraycoating method, a roll coating method, a brush coating method, a spongecoating method, a screen printing method, and an ink jet printingmethod.

Photocatalyst and Structure

The photocatalyst according to the exemplary embodiment contains or isformed from the titanium oxide particle according to the exemplaryembodiment.

A structure according to the exemplary embodiment contains the titaniumoxide particle according to the exemplary embodiment.

The photocatalyst according to the exemplary embodiment may be aphotocatalyst formed from only the titanium oxide particle according tothe exemplary embodiment, a photocatalyst obtained by mixing a promotorto the titanium oxide particle according to the exemplary embodiment, ora photocatalyst obtaining by fixing the titanium oxide particleaccording to the exemplary embodiment to a desired shape by using anadhesive or a pressure-sensitive adhesive.

From a viewpoint of photocatalyst activation, the structure according tothe exemplary embodiment preferably has at least the titanium oxideparticle according to the exemplary embodiment, on the surface.

The structure according to the exemplary embodiment preferably has thetitanium oxide particle according to the exemplary embodiment, as aphotocatalyst.

The structure according to the exemplary embodiment is preferably astructure in which at least the titanium oxide particle according to theexemplary embodiment is provided at at least a portion of the surface ofa base material, and is preferably a structure formed by applying thecomposition for forming a photocatalyst according to the exemplaryembodiment, to at least a portion of the surface of the base material.

In the structure, the amount of the applied composition for forming aphotocatalyst according to the exemplary embodiment is not particularlylimited, and may be selected in accordance with a desire.

Further, in the structure according to the exemplary embodiment, thetitanium oxide particle according to the exemplary embodiment may beadhered or fixed to the surface of the base material. However, from aviewpoint of durability of the photocatalyst, the titanium oxideparticle is preferably fixed to the surface of the base material. Afixing method is not particularly limited, and well-known fixing methodsare used.

As a base material used in the exemplary embodiment, various materialsare exemplified regardless of an inorganic material and an organicmaterial. The shape of the base material is also not limited.

Preferable examples of the base material include metal, ceramic, glass,plastic, rubber, stone, cement, concrete, textile, fabric, wood, paper,and combination thereof, a stacked member, and an object having at leastone coated film on the surface thereof.

Examples of the base material which is preferable from a viewpoint of ause include a building material, an exterior material, a window frame,window glass, a mirror, a table, dishes, a curtain, lens, a prism,exterior and painting of a vehicle, exterior of a mechanical device or aproduct, a dustproof cover and painting, a traffic sign, various displaydevices, an advertising tower, a sound insulation wall for road, a soundinsulation wall for railway, a bridge, exterior and painting of a guardrail, interior and painting of a tunnel, an insulator, a solar cellcover, a solar water heater collector cover, a polymer film, a polymersheet, a filter, an indoor signboard, an outdoor signboard, a vehiclelighting lamp cover, an outdoor lighting equipment, an air purifier, awater purifier, medical equipment, and a nursing care product.

EXAMPLES

The present invention will be more specifically described by usingexamples. However, the examples do not limit the present invention. “Apart” or “%” indicates a weight basis as long as particular statement isnot made.

Example 1

40% by weight of isobutyltrimethoxysilane with respect to thenot-treated titanium oxide particles is dropped into a dispersion inwhich a commercial anatase type titanium oxide particle (“SSP-20(manufactured by Sakai Chemical Industry Co., Ltd.)”, volume averageparticle diameter of 12 nm) is dispersed in methanol, so as to performreaction at 60° C. for one hour. Then, ejection and drying is performedat an outer port temperature of 120° C., thereby dry powder is obtained.Heating treatment is performed on the obtained dry powder in an electricfurnace at 400° C. for one hour, and thus a titanium oxide particle 1 isobtained.

Example 2

A titanium oxide particle 2 is obtained in the same manner as in Example1 except that isobutyltrimethoxysilane in Example 1 is changed tohexyltrimethoxysilane.

Example 3

A titanium oxide particle 3 is obtained in the same manner as in Example1 except that isobutyltrimethoxysilane in Example 1 is changed todecyltrimethoxysilane.

Example 4

A titanium oxide particle 4 is obtained in the same manner as in Example2 except that an added amount of hexyltrimethoxysilane in Example 2 ischanged from 40 parts to 50 parts.

Example 5

A titanium oxide particle 5 is obtained in the same manner as in Example2 except that the temperature in the electric furnace when driedparticulate powder in Example 2 is heated is changed from 400° C. to250° C.

Example 6

A titanium oxide particle 6 is obtained in the same manner as in Example1 except that the temperature in the electric furnace when driedparticulate powder in Example 1 is heated is changed from 400° C. to500° C.

Example 7

A titanium oxide particle 7 is obtained in the same manner as in Example2 except that an added amount of hexyltrimethoxysilane in Example 2 ischanged from 40 parts to 25 parts.

Example 8

A titanium oxide particle 8 is obtained in the same manner as in Example2 except that an added amount of hexyltrimethoxysilane in Example 2 ischanged from 40 parts to 75 parts.

Example 9

A titanium oxide particle 9 is obtained in the same manner as in Example2 except that the anatase type titanium oxide particle in Example 2 ischanged to commercial rutile type titanium oxide particle (“STR-100N(manufactured by Sakai Chemical Industry Co., Ltd.)”, volume averageparticle diameter of 16 nm).

Example 10

A titanium oxide particle 10 is obtained in the same manner as inExample 2 except that the anatase type titanium oxide particle inExample 2 is changed to an anatase type titanium oxide particle (volumeaverage particle diameter of 80 nm) prepared by a sol-gel method.

Example 11

A titanium oxide particle 11 is obtained in the same manner as inExample 2 except that an added amount of hexyltrimethoxysilane inExample 2 is changed from 40 parts to 10 parts.

Example 12

A titanium oxide particle 12 is obtained in the same manner as inExample 1 except that isobutyltrimethoxysilane in Example 1 is changedto methyltrimethoxysilane.

Example 13

A titanium oxide particle 13 is obtained in the same manner as inExample 1 except that isobutyltrimethoxysilane in Example 1 is changedto hexamethyldisilazane.

Example 14

A titanium oxide particle 14 is obtained in the same manner as inExample 1 except that 40 parts of isobutyltrimethoxysilane as a surfacetreatment agent in Example 1 are changed to 30 parts ofdodecyltrimethoxysilane.

Example 15

A titanium oxide particle 15 is obtained in the same manner as inExample 1 except that isobutyltrimethoxysilane in Example 1 is changedto phenyltrimethoxysilane.

Example 16

A titanium oxide particle 16 is obtained in the same manner as inExample 2 except that the temperature in the electric furnace when driedparticulate powder is heated in Example 2 is changed from 400° C. to180° C.

Example 17

A titanium oxide particle 17 is obtained in the same manner as inExample 2 except that the anatase type titanium oxide particle inExample 2 is changed to an anatase type titanium oxide particle (volumeaverage particle diameter of 200 nm) prepared by a sol-gel method.

Example 18

A titanium oxide particle 18 is obtained in the same manner as inExample 2 except that the anatase type titanium oxide particle inExample 2 is changed to an anatase type titanium oxide particle (volumeaverage particle diameter of 800 nm) prepared by a sol-gel method.

Example 19

A titanium oxide particle 19 is obtained in the same manner as inExample 1 except that hexyltrimethoxysilane in Example 10 is changed toisobutyltrimethoxysilane.

Example 20

A titanium oxide particle 20 is obtained in the same manner as inExample 1 except that isobutyltrimethoxysilane in Example 1 is changedto isopropyl triisostearoyl titanate (TTS, manufactured by AjinomotoCo., Inc.).

Example 21

A titanium oxide particle 21 is obtained in the same manner as inExample 1 except that isobutyltrimethoxysilane in Example 1 is changedto acetoalkoxyaluminum diisopropylate (AL-M, manufactured by AjinomotoCo., Inc., an alkoxy group in acetoalkoxy is an oxadecyloxy group).

Comparative Example 1

A commercial anatase type titanium oxide particle (“SSP-20 (manufacturedby Sakai Chemical Industry Co., Ltd.”, volume average particle diameterof 12 nm)) itself is used as a titanium oxide particle C1.

Comparative Example 2

A commercial rutile type titanium oxide particle (“STR-100N(manufactured by Sakai Chemical Industry Co., Ltd.”, volume averageparticle diameter of 16 nm)) itself is used as a titanium oxide particleC2.

Comparative Example 3

The commercial anatase type titanium oxide particle (“SSP-20(manufactured by Sakai Chemical Industry Co., Ltd.”, volume averageparticle diameter of 12 nm)) is heated at 400° C. in an electric furnacefor one hour, thereby a titanium oxide particle C3 is obtained.

Comparative Example 4

The commercial rutile type titanium oxide particle (“STR-100N(manufactured by Sakai Chemical Industry Co., Ltd.”, volume averageparticle diameter of 16 nm)) is heated at 400° C. in an electric furnacefor one hour, thereby a titanium oxide particle C4 is obtained.

Comparative Example 5

A titanium oxide particle C5 is obtained in the same manner as inExample 1 except that an added amount of isobutyltrimethoxysilane inExample 1 is changed from 40 parts to 5 parts.

Comparative Example 6

A titanium oxide particle C6 is obtained in the same manner as inExample 1 except that an added amount of isobutyltrimethoxysilane inExample 1 is changed from 40 parts to 120 parts.

Comparative Example 7

A titanium oxide particle C7 is obtained in the same manner as inExample 1 except that the temperature in the electric furnace when driedparticulate powder in Example 1 is heated is changed from 400° C. to600° C.

Comparative Example 8

A titanium oxide particle C8 is obtained in the same manner as inExample 1 except that the temperature in the electric furnace when driedparticulate powder in Example 1 is heated is changed from 400° C. to160° C.

Comparative Example 9

A titanium oxide particle C9 is obtained in the same manner as inExample 1 except that dried particulate powder in Example 1 is notheated.

Measurement

Regarding the particles obtained in the examples, ultraviolet-visibleabsorption spectrum characteristics are confirmed. The particles inExamples 1 to 21 and Comparative Examples 5 to 7 absorb light in a rangeof a wavelength from 400 nm to 800 nm. (Mark as “UV-Vis characteristics”in Tables 1 and 2: an absorbance of a wavelength of 450 nm, anabsorbance of a wavelength of 600 nm, and an absorbance of a wavelengthof 750 nm, respectively, when an absorbance of a wavelength of 350 nm isset to 1), the C/Ti element ratio on the surface of the particle by XPS,and the volume average particle diameter (in Table, marked as “D50v”)are measured in accordance with the above-described methods.

The surface of the particle obtained in each of the examples isirradiated with an ultraviolet ray having a wavelength of 352 nm and atan irradiation intensity of 1.3 mW/cm² at 25° C. for 20 hours. Then, theC/Ti element ratio on the surface of the particle by XPS is measured inaccordance with the above-described method and the reduced amount of theC/Ti element ratio before and after the irradiation with the ultravioletray is calculated.

Evaluation

Decomposing Ability (Photocatalyst Activation)

Decomposing ability is evaluated as photocatalyst characteristics in thevisible light region. Regarding evaluation of the decomposing ability,evaluation is performed by using decomposing ability (chromaticityvariation) of methylene blue. Specifically, the particles obtained ineach of the examples are dispersed in pure water containing 4 parts byweight of methanol, so as to cause solid concentration to be 2 parts byweight. Then, the dispersion is ejected and applied onto filter paper (5cm square: No. 5A manufactured by Advantech Co., Ltd.). Then, the paperis dried, and thus sample particles are uniformly adhered to the surfaceof the filter paper.

Then, a methylene blue diluted liquid obtained in a manner that a 2 wt %methylene blue aqueous solution is diluted and prepared 5 times inmethanol is ejected and applied onto the surface thereof. Then, dryingis performed, and thus a sample piece is prepared.

A test piece just after the test piece is prepared is continuouslyirradiated with visible light (10,000 LX (LUX)) for two hours by using alight emitting diode (LED) which performs irradiation with visible lighthaving a wavelength of 400 nm to 550 nm. The light emitting diode doesnot have an absorption wavelength region (wavelength of 400 nm to 800nm) of methylene blue. At this time, a 5-yen coin is disposed at thecenter portion of the irradiated surface of the test piece, and thus ablocked portion of the irradiation is formed.

Just after the test piece is prepared, hue of the test piece afterirradiation with visible light for two hours is measured by a spectralcolor difference meter “RM200QC (manufactured by X-Rite Inc.)”, and ΔE1and ΔE2 calculated by the following expression are obtained.

Chromaticity E is a value calculated by an expression ofE={(a*)²+(b*)²+(C*)²}^(0.5). Each of a*, b*, and C* represents a valuebased on an a*b*C* color system.ΔE1=(chromaticity of the irradiated surface after continuous irradiationwith visible light for two hours)−(chromaticity of the surface of a testpiece just after the test piece is prepared)  Expression:ΔE2=(chromaticity of the blocked surface of the irradiation aftercontinuous irradiation with visible light for two hours)−(chromaticityof the surface of the test piece just after the test piece isprepared)  Expression:

Thus, decomposing ability is evaluated based on a decoloring variationvalue ΔE=ΔE1−ΔE2. Evaluation criteria are as follows.

—Evaluation Criteria of Decomposing Ability—

-   -   A: 15%≤ΔE    -   B: 5%≤ΔE<15%    -   C: ΔE<5%

(Dispersibility (Particle Aggregation))

The dispersibility is evaluated as follows. 0.05 g of particles obtainedin each of the examples is put into a beaker, and 40 g of methyl ethylketone is added thereto. Then, particle diameter distribution afterdispersing is performed for 10 minutes in an ultrasonic dispersionmachine is measured by NANOTRACK UPA-ST (a dynamic light scattering typeparticle diameter measuring device manufactured by Microtrac Bel). Thus,evaluation is performed by distribution form of volume particle diameterdistribution. Evaluation criteria are as follows.

—Evaluation Criteria of Dispersibility—

-   -   A: one peak value in the volume particle diameter distribution        is provided, and dispersibility is good    -   B: two peak values in the volume particle diameter distribution        are provided, but the main peak value is equal to or more than        10 times the other peak value. Thus, actually, there is no        problem in dispersibility.    -   C: three peak values or more in the volume particle diameter        distribution are provided, and dispersibility is poor.

Dispersibility (Dispersion into Binder)

The dispersibility is evaluated as follows. 0.05 g of particles obtainedin each of the examples is put into a beaker, 1 g of a methyl ethylketone solution obtained by dissolving acrylic resin (Mw=10,000) atconcentration of 1.8 wt % is added, and the particles are sufficientlyblended. Then, 40 g of methyl ethyl ketone are added and particlediameter distribution after dispersing is performed for 10 minutes in anultrasonic dispersion machine is measured by NANOTRACK UPA-ST (a dynamiclight scattering type particle diameter measuring device manufactured byMicrotrac Bel). Thus, evaluation is performed by using a distributionform of volume particle diameter distribution. Evaluation criteria areas follows.

Evaluation Criteria of Dispersibility

-   -   A: one peak value in the volume particle diameter distribution        is provided, and dispersibility is good    -   B: two peak values in the volume particle diameter distribution        are provided, but the main peak value is equal to or more than        10 times the other peak value. Thus, actually, there is no        problem in dispersibility.    -   C: three peak values or more in the volume particle diameter        distribution are provided, and dispersibility is poor.

Decomposition Prevention Property of Binder

A decomposition prevention property of the binder is evaluated asfollows. 0.5 g of particles obtained in each of the examples is put intoa beaker, and 2 g of a methyl ethyl ketone solution obtained bydissolving acrylic resin (Mw=10,000) at concentration of 13 wt % areadded. After stirring, 1 mL is portioned by a glass pipette and this iswidely applied to a glass plate (50 mm×50 mm). Then, drying issufficiently performed, and thus a test piece is prepared. Two testpieces are prepared.

Then, one test piece is continuously irradiated with visible light(30,000 LX (LUX)) by using a light emitting diode (LED) which performsirradiation with visible light having a wavelength of 400 nm to 800 nm,for 30 hours. The other test piece is stored in a dark place.

Regarding a surface coating film of each of the test pieces which hasbeen stored in the dark place and has been irradiated with visible lightfor 30 hours, infrared spectroscopic peak intensity of a carbonyl group(C═O) in an acrylic polymer (binder) is measured by an infraredspectrophotometer FTIR-410 (manufactured by JASCO Corporation). Then, ΔTcalculated by the following expression is obtained.ΔT=(infrared spectroscopic peak intensity of carbonyl group (C═O) insample after irradiation with visible light for 30 hours)/(infraredspectroscopic peak intensity of carbonyl group (C═O) in sample stored indark place)  Expression:

The decomposition prevention property of the binder is evaluated byusing the value of ΔT which is an infrared peak intensity ratio of thecarbonyl group (C═O). Evaluation criteria are as follows.

Evaluation Criteria of Decomposition Prevention Property of Binder

-   -   A: 0.8≤ΔT    -   B: 0.6≤ΔT<0.8    -   C: ΔT<0.6

Tables 1 and 2 show a list of the details and evaluation results of eachof the examples.

TABLE 1 Before irradiation with ultraviolet ray Metal-containingcompound UV-Vis characteristics Added Heating Absorbance of Absorbanceof Absorbance of amount temperature wavelength wavelength wavelengthMaterial of particle Type M (wt %) (° C.) of 450 nm of 600 nm of 750 nmExample 1 Anatase type titanium oxide Isobutyl Si 40% 400 0.42 0.33 0.21Example 2 Anatase type titanium oxide Hexyl Si 40% 400 0.58 0.43 0.26Example 3 Anatase type titanium oxide Decyl Si 40% 400 0.56 0.42 0.25Example 4 Anatase type titanium oxide Hexyl Si 50% 400 0.60 0.45 0.29Example 5 Anatase type titanium oxide Hexyl Si 40% 250 0.24 0.16 0.07Example 6 Anatase type titanium oxide Hexyl Si 40% 500 0.35 0.23 0.13Example 7 Anatase type titanium oxide Hexyl Si 25% 400 0.30 0.20 0.11Example 8 Anatase type titanium oxide Hexyl Si 75% 400 0.59 0.43 0.25Example 9 Rutile type titanium oxide Hexyl Si 40% 400 0.60 0.44 0.28Example 10 Sol-gel titanium oxide Hexyl Si 40% 400 0.56 0.44 0.26Example 11 Anatase type titanium oxide Hexyl Si 10% 400 0.12 0.09 0.02Example 12 Anatase type titanium oxide Methyl Si 40% 400 0.31 0.21 0.13Example 13 Anatase type titanium oxide HMDS Si 40% 400 0.33 0.24 0.14Example 14 Anatase type titanium oxide Dodecyl Si 30% 400 0.55 0.40 0.23Example 15 Anatase type titanium oxide Phenyl Si 40% 400 0.25 0.18 0.11Example 16 Anatase type titanium oxide Hexyl Si 40% 180 0.18 0.12 0.08Example 17 Sol-gel titanium oxide Hexyl Si 40% 400 0.55 0.38 0.24Example 18 Sol-gel titanium oxide Hexyl Si 40% 400 0.50 0.38 0.21Example 19 Anatase type titanium oxide Isobutyl Si 40% 400 0.40 0.310.20 Example 20 Anatase type titanium oxide Isopropyl- Ti 40% 400 0.250.16 0.08 triisostearoyl Example 21 Anatase type titanium oxide diiso-Al 40% 400 0.31 0.21 0.12 propylate Before irradiation After irradiationwith ultraviolet ray with ultraviolet ray Evaluation XPS XPS Binder C/TiC/Ti Changed amount Dispersibility decomposition element D50v element ofC/Ti Decomposing (Particle prevention ratio (μm) ratio element ratioability aggregation) (Binder) property Example 1 0.95 12 0.16 0.66 A A AA Example 2 0.86 12 0.16 0.52 A A A A Example 3 1.05 12 0.16 0.62 A A AA Example 4 0.86 12 0.16 0.54 A A A A Example 5 1.16 12 0.16 0.26 A A AA Example 6 0.48 12 0.16 0.19 B A B A Example 7 0.58 12 0.16 0.22 A A BA Example 8 1.11 12 0.16 0.36 A A A A Example 9 0.95 16 0.16 0.40 A A AA Example 10 0.95 80 0.16 0.70 A A A A Example 11 0.35 12 0.16 0.12 B AB A Example 12 0.86 12 0.16 0.22 B A B A Example 13 0.90 12 0.16 0.14 BA B A Example 14 0.79 12 0.16 0.16 B A A A Example 15 1.16 12 0.16 0.21B B B A Example 16 1.18 12 0.16 0.21 B A A A Example 17 0.86 200 0.160.45 A A A A Example 18 0.74 800 0.16 0.36 A A A A Example 19 0.95 800.16 0.79 A A A B Example 20 0.88 12 0.60 0.28 B B B A Example 21 0.7612 0.40 0.36 B B B A

TABLE 2 Before irradiation with ultraviolet ray Metal-containingcompound UV-Vis characteristics Added Heating Absorbance of Absorbanceof Absorbance of amount temperature wavelength wavelength wavelengthMaterial of particle Type M (wt %) (° C.) of 450 nm of 600 nm of 750 nmComparative Anatase type titanium oxide None — None None 0 0 0 Example 1Comparative Rutile type titanium oxide None — None None 0 0 0 Example 2Comparative Anatase type titanium oxide None — None 400 0 0 0 Example 3Comparative Rutile type titanium oxide None — None 400 0 0 0 Example 4Comparative Anatase type titanium oxide Isobutyl Si  5% 400 0.02 0.010.01 Example 5 Comparative Anatase type titanium oxide Isobutyl Si 120% 400 0.60 0.43 0.26 Example 6 Comparative Anatase type titanium oxideIsobutyl Si 40% 600 0.06 0.03 0.01 Example 7 Comparative Anatase typetitanium oxide Isobutyl Si 40% 160 0.01 0 0 Example 8 ComparativeAnatase type titanium oxide Isobutyl Si 40% None 0 0 0 Example 9 Beforeirradiation After irradiation with ultraviolet ray with ultraviolet rayEvaluation XPS XPS Binder C/Ti C/Ti Changed amount Dispersibilitydecomposition element D50v element of C/Ti Decomposing (Particleprevention ratio (μm) ratio element ratio ability aggregation) (Binder)property Comparative 0.19 12 0.16 0.03 C C C A Example 1 Comparative0.19 16 0.16 0.03 C C C A Example 2 Comparative 0.16 12 0.16 0 C C C AExample 3 Comparative 0.16 16 0.16 0 C C C A Example 4 Comparative 0.1912 0.16 0.03 C C C A Example 5 Comparative 1.53 12 1.47 0.06 C B B AExample 6 Comparative 0.25 12 0.21 0.04 C C C A Example 7 Comparative1.32 12 1.26 0.05 C A A A Example 8 Comparative 1.50 12 1.44 0.06 C A AA Example 9

It is understood that the examples have decomposing ability better thanthat in the comparative examples, from the above results. Thus, it isunderstood that the examples show a high photocatalyst function even inthe visible light region in comparison to the comparative examples. Itis understood that the examples also secure dispersibility anddecomposition prevention property of the binder.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A titanium oxide particle, comprising: a core oftitanium oxide; and a metal compound having a hydrocarbon group, whichis bonded to a surface of the core through an oxygen atom, wherein thetitanium oxide particle absorbs light having a wavelength of 450 nm andlight having a wavelength of 750 nm, an element ratio C/Ti betweencarbon C and titanium Ti on a surface on the titanium oxide particles isfrom 0.3 to 1.2, and the element ratio of C/Ti on the surface of thetitanium oxide particle after irradiation with an ultraviolet ray havinga wavelength of 352 nm and at an irradiation intensity of 1.3 mW/cm² for20 hours is reduced in an amount from 0.1 to 0.9.
 2. The titanium oxideparticle according to claim 1, which has an absorption in a whole rangeof a wavelength of 400 nm to 800 nm in a visible absorption spectrum. 3.The titanium oxide particle according to claim 1, which is prepared bysubjecting a core of titanium oxide to a surface treatment with ametal-containing compound to obtain the titanium oxide particle, themetal-containing compound being a compound represented by R¹ _(n)SiR²_(m) wherein R¹ represents an aliphatic hydrocarbon group or an aromatichydrocarbon group which has 1 to 20 carbon atoms and is saturated orunsaturated, R² represents a halogen atom or an alkoxy group, nrepresents an integer of 1 to 3, m represents an integer of 1 to 3,provided that n+m=4 is satisfied, when n represents an integer of 2 or3, plural R¹'s may be the same or different, and when m represents aninteger of 2 or 3, plural R²'s may be the same or different.
 4. Thetitanium oxide particle according to claim 3, wherein R¹ is a straightchain shape saturated aliphatic hydrocarbon group.
 5. The titanium oxideparticle according to claim 3, wherein R¹ is a hexyl group.
 6. Thetitanium oxide particle according to claim 3, wherein R¹ is an aromatichydrocarbon group having 6 to 18 carbon atoms.
 7. The titanium oxideparticle according to claim 6, wherein R¹ is a phenyl group.
 8. Thetitanium oxide particle according to claim 3, wherein R² is an alkoxygroup having 1 to 10 carbon atoms.
 9. The titanium oxide particleaccording to claim 3, wherein R² is a methoxy group.
 10. The titaniumoxide particle according to claim 3, wherein R² is a chlorine atom. 11.The titanium oxide particle according to claim 1, which has a volumeaverage particle diameter of from 10 nm to 1 μm.
 12. A composition forforming a photocatalyst, comprising: the titanium oxide particleaccording to claim 1; and at least one compound selected from the groupconsisting of a dispersion medium and a binder.
 13. The composition forforming a photocatalyst according to claim 12, wherein the dispersionmedium contains water or an organic solvent.
 14. The composition forforming a photocatalyst according to claim 13, wherein the organicsolvent is an alcohol solvent.
 15. The composition for forming aphotocatalyst according to claim 12, wherein the binder comprises atleast one selected from the group consisting of a fluorine resin, asilicone resin, a polyester resin, and an acrylic resin.
 16. Thecomposition for forming a photocatalyst according to claim 12,comprising a coloring material included in the binder.
 17. Aphotocatalyst comprising the titanium oxide particle according toclaim
 1. 18. The photocatalyst according to claim 17, further comprisinga promotor.
 19. The photocatalyst according to claim 17, furthercomprising an antiseptic agent.
 20. The photocatalyst according to claim17, further comprising a thickener.